A known fluid control valve is disclosed in JP2003-184582A (see paragraphs [0014], [0015] and FIGS. 1 and 4) (i.e., hereinafter referred to as Patent reference 1). The fluid control valve disclosed in the Patent reference 1 is attached to a surge tank mounted to an intake system for a V-type multiple-cylinder engine. The surge tank is separated into two surge spaces by a partition wall. Odd numbered cylinders are provided to extend from one of the surge spaces and even numbered cylinders are provided to extend from the other of the surge spaces. A part of the partition wall is open to serve as a fluid passage. By operating a valve body by an actuation of an actuator to rotate between an open position and a closed position, a resonance frequency of the intake system is changed to attain supercharging effects in a wide engine driving range. In a case where an engine is operated in a state where the valve body is at the closed position, a pressure is alternately generated in the surge spaces which are separated by the partition wall because each cylinder sucks the air in a predetermined order. However, if a fluid leaks when the valve is at the closed position in those circumstances, the intake system cannot attain an expected resonance frequency, thereby degrading the supercharging effects.
As shown in FIG. 8, an elastic sealing member 117 of the fluid control valve disclosed in the Patent reference 1 includes a lip portion 119 having a V-shaped cross section which opens to a sealing surface 113. The lip portion 119 with the V-shaped cross section includes an outwardly directed lip portion 119s which is provided to protrude outwardly in a radial direction from a rim portion of the valve body and an inwardly directed lip portion 119t which is provided to protrude inwardly from the rim portion to a center portion of the valve body. In a state where a pressure is generated in a first surge space 107a, a tip end of the outwardly directed lip portion 119s structuring the V-shaped cross section is pushed to the sealing surface 113 to seal the valve body and the sealing surface 113. In a state where a pressure is generated in a second surge space 107b, a tip end of the inwardly directed lip portion 119t is pushed to the sealing surface 113 to seal the valve body and the sealing surface 113. In consequence, a sealing state is securely attained when the pressure is generated in either surge spaces which are separated via the partition wall.
Notwithstanding, according to the constructions of the fluid control valve disclosed in the Patent reference 1, because the portions structuring the V-shaped cross-section of the lip portion 119 are pressed to the sealing surface 113 simultaneously when the valve body is at the closed position, there is a risk that the lip portion 119 is sucked to the sealing surface 113 due to a vacuum pressure generated in a space S enclosed by the sealing surface 113 and inner side surfaces of the portions structuring the V-shaped cross-section of the lip portion 119. In a case where the lip portion 119 is sucked to the sealing surface 113, there is a risk that a switching of the valve to the open position by the actuator may not be stably performed and/or a drawback, that an actuator generating a greater rotational torque may be required, may be caused.
Further, according to the construction of the fluid control valve disclosed in the Patent reference 1, the portions structuring the V-shaped cross-section of the lip portion 119 is pressed against the sealing surface 113 by the pressure generating either at a first side or a second side of the partition wall when the valve body is at the closed position to be compulsorily deformed to further open a distance of the V-shaped portion. In consequence, a stress is concentrated to a fork portion constructing the V-shaped portion of the lip portion 119 by a pressing force caused by the pressure generated either at the first side or the second side of the partition wall, which may break the fork portion.
A need thus exists for a fluid control valve which is not susceptible to the drawback mentioned above.